Illumination system for a flat-panel picture display device

Abstract

The invention relates to an illumination system comprising an optical waveguide of an optically transparent material having an exit surface and a plurality of end faces, and a light source whose light is coupled into the waveguide via at least one end face of the waveguide. The waveguide further comprises polarizing means for polarizing the light emitted by the light source. The waveguide comprises at least two layers, of which one layer comprises an optically anisotropic material having refractive indices n e and n o and the other layer comprises an optically isotropic material having a refractive index n i , in which one of the refractive indices n e or n o is equal to n i . For the refractive indices, n e or n o should be equal or substantially equal to n i in order that polarization separation occurs at the interface between the isotropic and the anisotropic material. The invention also relates to a flat-panel picture display device including such an illumination system.

I claim: 
     
       1. An illumination system comprising: an optical waveguide of an optically transparent material having an exit surface and a plurality of end faces;   a light source opposite from one of the end faces and whose light can be coupled in at said end face of the optical waveguide; and   polarizing means for polarizing the light emitted by the light source, the waveguide having at least two layers, including:   one layer with an optically anisotropic material having refractive indices n e  and n o  ; and   another layer with an optically isotropic material having a refractive index n i , in which one of the refractive indices n e  or n o  is at least substantially equal to n i .   
     
     
       2. The illumination system of claim 1, wherein the refractive index n i  of the layer with isotropic material is substantially equal to the largest of the refractive indices n o  and n e . 
     
     
       3. The illumination system of claim 1 wherein the layer with anisotropic material is at the surface of the waveguide facing away from the exit surface. 
     
     
       4. The illumination system of claim 1 further comprising a collimating structure at the exit surface of the waveguide. 
     
     
       5. The illumination system of claim 4, wherein the collimating structure includes a microlens array. 
     
     
       6. The illumination system of claim 1 further comprising a reflector having a depolarizing effect on at least one end face remote from a light source. 
     
     
       7. The illumination system of claim 1 wherein the end faces of the waveguide are a collimator. 
     
     
       8. The illumination system of claim 7, wherein the collimator end faces include a cylindrical lens. 
     
     
       9. The illumination system of claim 1, wherein the optically anisotropic material includes an anisotropic polymer gel or an anisotropic polymer network. 
     
     
       10. A flat-panel picture display device comprising: an illumination system provided with a picture display panel for modulating the direction of polarization of light emitted by the illumination system in conformity with picture information to be displayed; and   an analyzer; and   wherein the illumination system includes:   an optical waveguide of an optically transparent material having an exit surface and a plurality of end faces;   a light source opposite from one of the end faces and whose light can be coupled in at said end face of the optical waveguide; and   polarizing means for polarizing the light emitted by the light source, the waveguide having at least two layers, including:   one layer with an optically anisotropic material having refractive indices n e  and n o  ; and   another layer with an optically isotropic material having a refractive index n i , in which one of the refractive indices n e  or n o  is at least substantially equal to n i .   
     
     
       11. The device of claim 10, wherein the refractive index n i  of the layer with isotropic material is substantially equal to the largest of the refractive indices n o  and n e . 
     
     
       12. The device of claim 10, wherein the layer with anisotropic material is at the surface of the waveguide facing away from the exit surface. 
     
     
       13. The device system of claim 10 further comprising a collimating structure at the exit surface of the waveguide. 
     
     
       14. The device system of claim 13, wherein the collimating structure includes a microlens array. 
     
     
       15. The device of claim 10 further comprising a reflector having a depolarizing effect on at least one end face remote from a light source. 
     
     
       16. The device of claim 10, wherein the end faces of the waveguide are collimator. 
     
     
       17. The device of claim 16, wherein the collimator end faces include a cylindrical lens. 
     
     
       18. The device of claim 10, wherein the optically anisotropic material includes an anisotropic polymer gel or an anisotropic polymer network.